1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device. More specifically, the present invention relates to a semiconductor device having a shield electrode connected to a source electrode and to a method of manufacturing the semiconductor device.
2. Background Art
As a conventional MOSFET effective in improving gain, a laterally diffused metal oxide semiconductor (LDMOS) for example is known. In the LDMOS, a source electrode is extended so as to cover a gate electrode. A Faraday shielding effect is thereby produced to achieve a reduction in gate-drain capacitance (Cgd) and, hence, an increase in gain.
Another structure for reducing the gate-drain capacitance is known in which a shield electrode is formed between a gate electrode and a drain electrode on a substrate with insulating film interposed between these electrodes. Also in this structure, the gate electrode and the drain electrode are separated by the shield electrode to reduce the gate-drain capacitance and to thereby improve the maximum stable gain (MSG).
A technique of forming a recess structure in an ion implanted portion of a cap layer and forming an offset gate electrode adjacent to this ion implanted portion has also been disclosed (see, for example, Japanese Patent Laid-Open No. 2000-124227). In this technique, the distance between the gate electrode and the drain electrode is increased to minimize the capacitance Cgd.
The gate-source capacitance (Cgs) is increased in a case where, as in the above-described conventional structure, a source electrode or a shield electrode connected to a source electrode is formed on a gate electrode with insulating film interposed therebetween. A semiconductor device having electrodes formed as described above is thought to have a deterioration in characteristics, e.g., an increase in noise factor (NF) when used in a low-noise amplifier. Therefore, an increase in gate-source capacitance accompanying a reduction in gate-drain capacitance is undesirable.
In a case where a T-gate electrode structure is used as a gate electrode, not only the capacitance between the gate electrode and the drain electrode but also the capacitance between the gate electrode and the semiconductor layer is an influential factor in determining the gate-drain capacitance. In the conventional art, however, it is difficult to reduce the capacitance between the gate electrode and the semiconductor layer since a source electrode or a shield electrode is laminated on the gate electrode.